I. Field
The present invention relates generally to communication, and more specifically to techniques for decoding a control channel in a wireless communication system.
II. Background
A terminal in a wireless communication system (e.g., a cellular system) is typically designed to operate in one of several modes, such as active and idle, at any given moment. In the active mode, the terminal can actively exchange data with one or more base stations in the system (e.g., for a voice or data call). In the idle mode, which is also referred to as standby mode, the terminal typically monitors a paging channel for messages alerting the terminal to the presence of an incoming call. The terminal may also monitor a broadcast control channel for messages to update its system parameters.
In the idle mode, the terminal continues to consume power in order to sustain circuitry needed to monitor signals transmitted from base stations in the system. The terminal (e.g., a cellular phone) may be portable and powered by an internal battery. Power consumption by the terminal in the idle mode decreases the available battery power, which then shortens “standby” time between battery recharges and “talk” time when a call is placed or received. Therefore, it is highly desirable to minimize the terminal's power consumption while in the idle mode in order to prolong battery life.
In one technique for reducing power consumption in the idle mode, messages (if any) are sent on the paging channel to the terminal at designated times. For example, in a Global System for Mobile Communications (GSM) system, each terminal is assigned specific Time Division Multiple Access (TDMA) frames for its paging channel, and messages are sent to the terminal in these TDMA frames. In GSM, a paging message (i.e., a message to be sent on the paging channel) is first encoded into a coded data block. The bits within the coded data block are then interleaved (i.e., reordered) and partitioned into four “output blocks”. The four output blocks are then transmitted on the paging channel as four “bursts” in four consecutive TDMA frames.
In a GSM system, a terminal can periodically rather than continuously monitor the paging channel for messages from the base stations. Conventionally, the terminal wakes up from a “sleep” state prior to the first designated TDMA frame for the paging channel, enters an “awake” state and receives all four bursts sent for a paging message, and processes (i.e., concatenates, deinterleaves, and decodes) these four bursts to recover the paging message. (The sleep and awake states are also referred to as “inactive” and “active” states, respectively.) The terminal would then revert back to the sleep state if additional communication is not required and would remain in the awake state if the recovered paging message indicates that additional actions need to be performed. In the time period between successive presences in the awake state, the terminal is in the sleep state and powers down as much circuitry as possible in order to conserve power.
A key benchmark for commercial cellular phones is standby time. Standby time is a function of (1) the amount of time spent in the awake state, (2) the amount of current spent while in the awake state, and (3) the amount of current spent while in the sleep state. The amounts of current spent in the sleep and awake states are determined by the specific design of the phone. However, for any given phone design, longer standby time may be achieved by reducing the amount of time spent in the awake state.
There is therefore a need in the art for techniques to shorten the amount of time needed to receive messages on the paging channel so that standby time can be improved.